Eccentric gearbox

ABSTRACT

An eccentric gearbox with selectable large speed ratio, in this gearbox many eccentric gear ( 8, 12, 16 ) pairs are assembled in parallel, and are connected to a common input shaft ( 1 ) and a common output shaft (2). In every gear pair ( 8, 12, 16 ), one gear keeps its orientation fixed with respect to a fixed part called as fixed gear ( 8, 12, 16 ) and another gear that rotates about its own axis is called as moving gear ( 7, 11, 15 ). Difference in number of teeth on the two gears of a gear pair is kept to one tooth or more. Through proper selection of a particular gear pair any speed ratio can be selected. In this way, it is possible to make a compact gearbox, with multiple large speed ratios. Such a gear box can be used in automobiles, robot manipulators, earth moving equipments, space applications, toys, hand held tools and many other applications.

TECHNICAL FIELD

This invention deals with large speed ratio eccentric gearbox withselectable speed ratio. In this gearbox many eccentric gear pairs areassembled in parallel, and are connected to a common input shaft and acommon output shaft. In every gear pair, one gear called fixed gearkeeps its orientation unchanged with respect to a fixed part and anothergear that rotates about its own axis is called as moving gear. The pointof contact is moved on to the pitch circle of the fixed gear throughsome mechanism connected and the moving gear is connected to an outputshaft. Difference in number of teeth on the two gears of an eccentricgear pair is kept to one tooth or more. Through proper selection of aparticular gear pair any speed ratio from available speed ratios can beselected. In this way, it is possible to make a compact gearbox, withmultiple (two or more) speed ratios, to have large speed ratios betweeninput and output shafts. These types of gearboxes are useful inautomobiles, and in many other applications where turbines are usedmainly as prime movers. Such a gear box can be used in automobiles,robot manipulators, earth moving equipments, space applications, toys,hand held tools and in many other applications.

BACKGROUND ART

Existing patents:

-   -   U.S. Pat. No. 3,996,816, dated Dec. 14, 1976, titled “Harmonic        Drive”.    -   U.S. Pat. No. 3,546,972, dated Dec. 15, 1970, titled “Profile        shifted involute internal gearing”.    -   U.S. Pat. No. 5,324,240, dated Jun. 28, 1994, titled “Eccentric        Gear System”.

All the above-mentioned inventions deals with single speed ratio geardrives. In all these inventions it is difficult to have multiple speedratio gearbox, from which a specific gear ratio can be selected. Byusing existing eccentric gear drives with turbines as a prime mover, itmay be necessary to use a conventional gearbox in series with theeccentric drive.

This invention is based on the work done and applied for internationalpatent bearing the international patent application numberPCT/IN01/00150 dated Aug. 29, 2001; configuration 2 and configuration 4are specifically used for present work. Using the configurations 2 and 4it is possible to make an eccentric gearbox to have multiple (two ormore) high speed ratios, any of the available speed ratios can beselected between input and output shaft by employing a suitable gearengagement mechanism. Though eccentric gearbox with any number of speedratios can be made with following methodology, only three speed ratiogearboxes are explained below.

DEFINITIONS:

Internal gear—A circular gear with internal teeth.

External gear—A circular gear with external teeth.

Fixed gear—The gear with fixed orientation.

Moving gear—The gear that rotates about its own axis.

Pitch circle—A reference circle on the plane normal to the rotationalaxis of the gear, the diameter of the pitch circle is used forcalculations.

Pitch Cylinder—A cylinder, co-axial to the rotational axis of the gear,that passes through the pitch circle of the gear. As most of the timethe gear cross section is referred, only pitch circle is referred in theexplanation that follows.

Point of contact—Theoretical common point on the pitch circles of thetwo meshing gears. The two pitch circles are tangential to each other onthis point.

Line of contact—Theoretical common line on the pitch cylinders of thetwo meshing gears. The two pitch cylinders are tangential to each otheron this line. This line is always parallel to the axes of the two gearsand passes through the point of contact. As most of the time the gearcross section is referred, only point of contact is referred in theexplanation that follows.

Eccentricity—Half the difference between the pitch circle diameters ofthe two meshing gears forming eccentric gear pair as in FIG. 1, FIG. 2and FIG. 3. The eccentricity should preferably be same for all eccentricparts related to a particular gear pair.

Introduction:

A gearbox with large speed ratio is very useful. This type of gearboxuses eccentric gear pair for obtaining large speed ratio; this makesit-very compact in size for large speed ratio. With an eccentricgearbox, it may be possible to use a turbine as a prime mover forautomobiles and for many other applications, without use of conventionalgearbox. Use of such a gearbox can make very compact turbine-gearboxunit and can replace the conventional reciprocating engine-gearbox unitin future. An eccentric gearbox can allow utilizing the benefits ofusing turbine over the use of reciprocating internal combustion engine.

The working of such an eccentric gearbox is explained with the help ofthree drawings. These three drawings as listed below, give details ofthree different possible configurations of such a gearbox.

FIG. 1—Schematic sectional view of a three speed eccentric gearbox, withexternal gears as fixed gears and internal gears as moving gears. Inputshaft is connected to the eccentrics and output shaft is co-axiallyconnected to the internal gears.

FIG. 2—Schematic sectional view of a three speed eccentric gearbox, withexternal gears as moving gears and internal gears as fixed gears. Inputshaft is connected to the eccentrics and output shaft is connected tothe external gears.

FIG. 3—Schematic sectional view of a three speed eccentric gearbox, withexternal gears as moving gears and internal gears as fixed gears. Inputshaft is connected to the additional driving gears and output shaft isconnected to the external gears.

PRINCIPLE OF OPERATION

In FIG. 1, 1 is the input shaft, which is supported by the fixed member4 at one end and output shaft 2 at the other end. Supporting disc 5gives additional support to the input shaft. Output gear assembly 6rotates freely in between 4 and 5. The input shaft rotates freely at thesupport by disc 5. The input shaft rotates freely in 4 and 2. The outputshaft 2 and output gear assembly 6 is freely rotating with respect tothe fixed part 4. Symbolic gear engagement mechanism 3 is placed toconnect one of many (actual number of eccentrics is equal to that ofeccentric gear pairs) eccentrics 10, 14, and 18 to the input shaft.These eccentrics 10, 14, 18 are guiding fixed gears 8, 12, 16 and arefreely rotating in the gears 8, 12, 16. The gears 8, 12, 16 are kept insame orientation through the eccentrics 9, 13 and 17 which are eitherfixed or free to rotate on the shaft 19. There are minimum three similarassemblies of shaft 19 and eccentrics 9, 13 and 17. If the eccentrics 9,13 and 17 are free to rotate on the shaft 19, then the shaft can befixed to the supporting disc 5 and to the fixed member 4, otherwise theshaft should be free to rotate in supporting disc 5 and fixed member4.This shaft 19 and the eccentrics 9, 13, 17 are arranged at minimumthree places in such a way that all axes of the shafts 19 are parallelbut all are not In the same plane. Shafts 19 are also supported by disc5. Internal gear rims 7, 11, 15 are mounted on 6 and thus connected tothe output shaft 2. Eccentricities of 9, 13 and 17 are independent ofeach other. Eccentricity of all 9's and 10 must be approximately same.Similarly eccentricity of all 13's and all 17's should be approximatelysame as that of 14 and 18 respectively. Eccentrics 10, 14 and 18 are puton shaft 1 in such a way that their axial movement along axis Al isrestricted. Only one of the eccentrics 10, 14, 18 is engaged to shaft 1at a time through gear engagement mechanism 3 and other two are free torotate on shaft 1.

When input shaft 1 is rotated the eccentric 14 (FIG. 1) also rotates,this forces axis of gear 12 to revolve around axis A1 and thus the pointof contact is forced to move on the pitch circle of the fixed gear 12.Three numbers of eccentric 13 maintain the orientation of the gear 12.The gear rim 11 and thus output shaft 2 rotates about axis A1. If gear12 has N number of teeth and gear rim 11 has M number of teeth, whereM>N, then the speed ratio obtained is M:(M−N).

In FIG. 1, it is also possible to rigidly connect the eccentrics 10, 14and 18 on to the input shaft I and use a gear engagement mechanism toengage one of the gear rims 7, 11 and 15 with the output shaft assembly6. Other two gear rims, which are not engaged to the output shaftassembly 6, should be free to rotate with respect to the output shaftassembly 6. Gear pair 7, 8, gear pair 11, 12 and gear pair 15, 16 arethe eccentric gear pairs in FIG. 1. Theoretical lines of contact fordifferent gear pairs are shown by 20, 21 and 22 in FIG. 1. Joint betweengear rims 7, 11, 15 and the output shaft assembly 6 is not shown in theFIG. 1.

In FIG. 2, Input shaft 4, which rotates freely in fixed part 3, ~isrigidly connected to eccentrics 7, 10 and 13. There are minimum threesuch similar shaft assemblies comprising of shaft 4 and eccentrics 7, 10and 13. Axes of all the shafts 4 are parallel but all are not in thesame plane. One of the shafts 4 is used as input shall Eccentrics 7, 10and 13 on shaft 4, other than on the input shaft are either free torotate or rigidly connected to the shaft 4. On the shaft 4, which isused as input shaft, all the eccentrics 7, 10 and 13 are rigidly fixed.In the case where the eccentrics 7, 10 and 13 rotate freely on shaft 4,the shaft 4 can be fixed to part 3. Internal gear 5, 8 and 11 are heldin S unchanged orientation with the help of eccentrics 7, 10 and 13respectively. Eccentricities of 7, 10 and 13 are independent of eachother but all the 7s should have approximately same eccentricity,similarly all 10s and all 13s should also have approximately sameeccentricity respectively. External gears 6, 9 and 12 are free to rotateon the output shaft 1. One of the external gears 6, 9 and 12 can beengaged to output shaft 1 at a time by gear engagement mechanism 2.Shaft 4 and shaft 1 are supported in fixed body 3. Shaft 1 rotates freewith respect to the fixed body 3. Gear engagement mechanism 2 can selectany of the gear pair 5, 6, gear pair 8, 9 and gear pair 11, 12. As shownin the FIG. 2, if internal gear has M number of teeth and external gearhas N number of teeth, where M>N, then the speed ratio obtained isN:(M−N).

In a different configuration based on FIG. 2, it is possible to keep theeccentrics 7, 10 and 13 to rotate freely on the input shaft 4 and usesuitable engagement mechanism to engage only one of the eccentrics 7, 10and 13 with the input shaft 4, in such case all other eccentrics 7, 10and 13 are free to rotate on the respective shaft 4. In this case allthe moving gears 6, 9 and 12 are to be fixed with the output shaft 1.Gear pair 5, 6, gear pair 8, 9 and gear pair 11, 12 are the eccentricgear pairs in FIG. 2. Theoretical lines of contact for different gearpairs are shown by 14, 15 and 16 in FIG. 2.

In FIG. 3, three driving gears 17, 18 and 19 are mounted on input shaft1 in such a way that at any time only one of the driving gears can beengaged to shaft 1 through symbolic gear engagement mechanism 3, otherdriving gears rotate freely on the shaft 1. Output shaft 2 is rigidlyconnected to the three external moving gears 7, 11 and 15. Threeeccentrics 5, 9 and 13 are either fixed or free to rotate on the supportshaft 4. Shaft 4 is free to rotate with respect to the fixed support 20,21, if any of the eccentrics 5, 9 and 13 is fixed on to the shaft 4. Ifthe eccentrics 5, 9 and 13 are freely rotating on the shaft 4, then theshaft 4 can be fixed rigidly to the fixed support 20, 21. Minimum threeassemblies of shaft 4 and the eccentrics 5, 9 and 13 maintain theorientation of the internal gear rims i.e. the fixed gears, 6, 10 and14. The axes of these three similar assemblies of shaft 4 and eccentricsare parallel but not all are in the same plane. The point of contactbetween the gear pair 6, 7, gear pair 10, 11 and gear pair 14, 15 aremoved by eccentric discs 8, 12 and 16 respectively. These eccentricdiscs 8, 12 and 16 are rigidly connected to gears driven by drivinggears 17, 18 and 19. The axes of rotation of these driven gears and theeccentric discs 8, 12 and 16 are coincident with the axis of the outputshaft 2. These driven gears and the eccentric discs are free to rotateon the output shaft 2. The eccentric discs 8, 12 and 16 are free torotate with respect to the internal gear rims 6, 10 and 14 respectively,and thus move the point of contact on the pitch circle diameter of thefixed gears.

In another possibility, in FIG. 3, all the driving gears 17, 18 and 19can be fixed to the input shaft 1 and the symbolic gear engagementmechanism 3 can be used to engage only one of the moving gears 7, 11 and15 to output shaft 2, other two moving gears are free to rotate on theoutput shaft 2. As shown in the FIG. 3, if internal gear has M number ofteeth and external gear has N number of teeth, where M>N, then the speedratio obtained between the eccentric disc assembly and the output shaftis N:(M−N). It is important here that the eccentricities of theeccentric disc and the eccentrics should be approximately same for aparticular gear pair, otherwise the eccentricities of the eccentrics areindependent of each other. Gear pair 6, 7, gear pair 10, 11 and gearpair 14, 15 are the eccentric gear pairs in FIG. 3. Theoretical lines ofcontact for different gear pairs are shown by 22, 23 and 24 In FIG. 3.

In all the above-mentioned gearboxes additional eccentrics, eccentricparts and related identical gears, gear rims or eccentric gear pairs canbe used simultaneously at appropriate phase difference. This may reducevibration and increase balancing in the gearbox. For the parts, whichare free to rotate, appropriate use of bearings will reduce friction. Inabove description gear teeth are not shown for simplicity ofunderstanding. It is possible to employ two gear engagement mechanismsinstead of one, this will make only one gear pair to get engaged at atime, other gear pair will be totally out of engagement, and thus mayincrease the life of the gearbox; this may introduce high impact at thetime of changing the engaged gear pair. Proper lubrication scheme has tobe worked out as per the specific application.

Advantages of the Eccentric Gearbox:

In an automobile if a turbine is to be used then immediately after theturbine output shaft one high ratio gear reduction is necessary. Afterthis high ratio gear reduction conventional gearbox is to be used. Thismakes the total system unnecessarily bulky, instead, if the eccentricgearbox is used it will eliminate the use of conventional gearbox andwill make the system more compact. In this type of eccentric gearbox, itis possible to have more than one speed ratios.

Disadvantages:

As many eccentrics are used and high input speed is involved, balancingof the gearbox has to be carried out very carefully.

1. An eccentric gearbox in which each external gear of the eccentricgear pairs, use minimum three eccentrics to maintain its orientation;the external gears are connected to the input shaft through eccentricsto guide the point of contact on the external gears and have their axesrevolve around the axis of the input shaft; a common shaft is used tomount one of the eccentrics for each external gear used to maintain theorientation of the external gear; minimum three such common shafts areused to maintain the orientation of the external gears; internal gearrims are connected to the output shaft assembly and are coaxial with theoutput shaft; the output shaft assembly is free to rotate with respectto the fixed part; output shaft and the input shaft are coaxial;eccentrics connected to the same external gear have approximately sameeccentricity; eccentrics connected to different external gears may havedifferent eccentricities; by selecting different eccentric gear pairs,different speed ratios are selected between the input shaft and theoutput shaft.
 2. An eccentric gearbox as claimed in claim 1 in which oneof the common shafts, on which the eccentrics are mounted to maintainthe orientation of the external gears, is used as input shaft; theshaft, which was stated as input shaft in claim 1 and is coaxial to theoutput shaft, is used to support the eccentrics for guiding the externalgear, the eccentrics used for guiding the external gear are free torotate on the supporting shaft.
 3. An eccentric gearbox as claimed inclaims 1 and 2 in which a gear engagement mechanism is used to engage ata time only one of the eccentrics, mounted on the input shaft, to theinput shaft; other eccentrics on the input shaft are free to rotate withrespect to the input shaft; all the internal gear rims are rigidlyconnected to the output shaft assembly.
 4. An eccentric gearbox asclaimed in claims 1 and 2 in which a gear engagement mechanism is usedto engage at a time only one internal gear rim to the output shaftassembly, other internal gear rims are free to rotate with respect tothe output shaft assembly; all the eccentrics mounted on the inputshaft, are rigidly connected to the input shaft.
 5. An eccentric gearboxin which every internal gear of the eccentric gear pair uses minimumthree eccentrics to maintain its orientation; axes of internal gearrevolve around axis of the output shaft; the external gears arecoaxially connected to the output shaft; internal gears are connected tothe input shaft assembly through eccentrics; eccentrics connected to thesame internal gear have approximately same eccentricity; eccentricsconnected to different internal gears may have different eccentricities;by selecting different gear pairs, different speed ratios are selectedbetween the input shaft and the output shaft.
 6. An eccentric gearbox asclaimed in claim 5 in which one of the eccentrics used for maintainingorientation of individual internal gears are mounted on a common shaft,and minimum three such common shafts are used; one of these shafts, withappropriate modification, is used as input shaft; these eccentrics arefree to rotate on individual common shaft and a gear engagementmechanism is used to engage the input shaft at a time to only one ofmany eccentrics on the input shaft; external gears are rigidly connectedto the output shaft and are coaxial to the output shaft.
 7. An eccentricgearbox as claimed in claim 5 in which one of the eccentrics for eachinternal gear, used to maintain the orientation of the internal gears,are mounted on a common shaft, and minimum three such common shaftassemblies are used; one of these shaft assemblies on which theeccentrics are rigidly mounted is used as input shaft; external gearsare mounted on to the output shaft assembly and are coaxial to theoutput shaft; these external gears are free to rotate on the outputshaft and a gear engagement mechanism is used to engage the output shaftat a time to only one of the external gears on the output shaft
 8. Aneccentric gearbox in which the internal gears of the eccentric gearpairs use minimum three eccentrics to maintain their orientation; theexternal gears are coaxially connected to the output shaft; all theeccentrics connected to the same internal gear have approximately sameeccentricity; eccentrics connected to different internal gears may havedifferent eccentricities; by selecting different eccentric gear pairs,different speed ratios are selected between the input shaft and theoutput shaft; number of, suitable spur gears, equal to that of internalgears are mounted on the input shaft; these spur gears drive the drivengears; these driven gears are coaxial to the axis of the output shaft;these driven gears are connected to separate eccentric disc, one foreach internal gear, which guides the internal gears and thus the axis ofthe internal gear is guided to revolve around the axis of the outputshaft.
 9. An eccentric gearbox as claimed in claim 8 in which thedifferent eccentrics, used to maintain the orientation of the individualinternal gears, are mounted on a common shaft and are either fixed tothe shaft or free to rotate on the shaft; minimum number of such commonshafts used is three.
 10. An eccentric gearbox as claimed in claims 8and 9 in which the spur gears, that are mounted on the input shaft arefree to rotate on the shaft, only one of the gears at a time is engagedto the input shaft by gear engagement mechanism; external gears of theeccentric gear pairs are rigidly connected to the coaxial output shaft.11. An eccentric gearbox as claimed in claims 8 and 9 in which the spurgears are rigidly mounted on the input shaft; external gears of theeccentric gear pairs are coaxially connected to the output shaft and arefree to rotate on the output shaft; at a time only one of the externalgears of the eccentric gear pairs is engaged to the output shaft by gearengagement mechanism.
 12. An eccentric gearbox as claimed in claims 8and 9 in which one of the common shafts having the eccentrics used formaintaining the orientation of the individual internal gear, is used forgear engagement mechanism; all the eccentrics on this shaft, used formaintaining orientation of the internal gear are free to rotate on theshaft; only one of the eccentric is engaged at a time to the shaft bygear engagement mechanism.
 13. An eccentric gearbox as claimed in claims1 to 12 in which two gear engagement mechanisms are used appropriatelyas to engage only one eccentric gear pair at a time between the inputand output shaft; gears of other eccentric gear pairs are not engaged toeither input shaft or output shaft.
 14. An eccentric gearbox as claimedin claims 1 to 13 in which more than one identical eccentric gear pairsare used; with the help of additional eccentrics or some othermechanism, one or more eccentric gear pairs are engaged simultaneouslyto input and output shafts.
 15. An eccentric gearbox as claimed in claim1 to 14 in which the input shaft is used as output shaft and the outputshaft is used as input shaft.
 16. An eccentric gearbox as claimed in theclaims 1 to 15 in which one or more eccentric gear pairs are used forgetting different speed ratios between input and output shafts.
 17. Aneccentric gearbox as claimed in the claims 1 to 16 in which suitablelubrication scheme and bearings are used appropriately for reducingfriction.
 18. An eccentric gearbox as claimed in the claims 1 to 17;which is used for obtaining multiple speed ratios between input andoutput shaft so that any one of the speed ratios can be selected foruse.